lit: The Habitable Epoch of the Early Universe

by A. Loeb.
That's a fantastically crazy paper (by A. Loeb, who's one of the best known names in areas as diverse as gravitational microlensing/black hole evolution/reionisation and 21 cm signal/high-z GRBs/Event Horizon telescope, and many others). He's written several papers about wild ideas before: exploring the (sad and very distant) future of observational cosmology, bio-markers in white dwarf planets' atmospheres, planets of hypervelocity stars, search of artificially-illuminated objects in and beyond the Solar System and cosmology measurements from hypervelocity stars which shows that not all is lost for the future cosmologists.
In this paper he looks at the dawn of the Universe, when it was only ~15 million year old. A. Loeb points out that the temperature of the cosmic microwave background was roughly around 0-30 C then, and therefore liquid water could have existed on any solid surface, meaning that there might have been conditions suitable to life as we know it. In order to form any rocky planet one needs to explode some massive stars before (to get some heavier elements like oxygen, iron, silicium, etc, which are what rocky planets are made of). At that time we're left with the formation of the very first stars in the very first, tiny, dark matter haloes at the far end of the density distribution. Calculations show that the number of such protogalaxies was incredibly small at these redshifts.
However, if we assume that the initial density distribution was not perfectly Gaussian (there are many theories explaining why it might have been the case, although Planck and other observations haven't found any proof of non-gaussianity yet), there might have been some haloes that had formed massive stars by that time.
It's a marvelous article, although AFAIK, it takes much longer than a few Myr for rocky planets to assemble from accretion disks of stars (and cool down due to the decay of radioactive elements..). But think of it: at some time in the history of the Universe the outer space was warm (and at least a million times denser than now).

lit: The Zeldovich approximation: key to understanding Cosmic Web complexity

Hidding, Shandarin et al. 2013: seems interesting, modelling the structure of the cosmic web.

lit: TFR at z=2.2 with SINFONI IFU

Cresci et al. 2013 -- they also use genetic algorithms for velocity field modelling.

lit: The power spectrum dependence of dark matter halo concentrations

Eke et al. 2001

lit: testing CDM with low-mass TFR

Blanton et al. 2008.

lit: TF as a constraint on the temperature of WDM

Constraints on the temperature of Warm Dark Matter from the Galaxy Stellar Mass Function and Tully-Fisher Relation by Kang, Maccio, Dutton. One more reason why TFR is important!

lit: Probability distributions of ellipticity

My pick for the weekly meeting: On the Probability Distributions of Ellipticity, by Viola et al. A review from the weak lensing perspective.

talk: assembly bias

I had volunteered to give a presentation on 'Detection of assembly bias' by Wang, Weinmann, de Lucia and Yang. It went pretty well today, here are the slides. It explains the difference between galaxy bias, halo bias and assembly bias. As one of my supervisors puts it, 'not good news'.

A colloquium by S. White

This morning I attended a talk on the Planck results by S. White, who contributed a lot to the current theories of cosmology and structure formation (White and Rees 1978, the NFW paper, etc.).
It was a brilliant talk, here are some things that stuck:
-- the strongest evidence we have for the existence of the dark matter does not come from rotation curves, but from CMB measurements instead!
-- the Planck team was able to do background subtraction very well because they had data from several channels: maps of synchro emission at radio frequencies and dust maps at FIR. Only 3% of the sky had to be interpolated.
-- Planck has the best dust maps of all time due to the previous point.
-- the mass map of the Universe from gravitational lensing measurements is incredible, and strongly correlates with cluster locations from the S-Z effect.
-- the spectral index n of the H-Z spectrum is not equal to 1 (this was news to me, I thought it should be close), but is near 0.96.
-- sigma_8 is less than 1 too (0.83, if I remember correctly)
-- there are issues w/ Planck-WMAP-SPT inter-calibration
-- the CMB is the edge of the visible Universe -- this is obvious, but I hadn't thought of it this way before.
-- there still are anomalies: the cold spot, differences of amount of structure between hemispheres, some structure that is compatible with a rotating Universe

lit: Where do the dwarf galaxies go?

I've just attended a colloquium by J. Navarro of the NFW fame, which was really related to my current reading list. I'm writing an introductory chapter on hierarchical galaxy assembly for my thesis at the moment.
One unsolved problem of LCDM cosmology is the apparent lack of dwarf galaxies: simulations and statistical frameworks (such as EPS) predict that we should see a large number (hundreds) of dwarf galaxies around each bright galaxy such as the Milky Way, but we only know of a dozen. Same with Andromeda.
J. Navarro also showed some puzzling properties of local dwarfs, for example, the fact that their star formation histories are wildly different. Some formed all their gas 10 or so Gyr ago, some had a starburst recently, and some have double-peaked SFH's. He presented the work of his student which could explain it: the CLUES simulation shows that a combination of interaction with the collapsing cosmic web, mergers of dwarfs and reionisation stripping can in principle explain this. Some dwarfs lost their gas simply because they moved too fast through the cosmic web. The remainders of such galaxies may be just too faint for us to see.

Daily Paper #13: the σ_8 parameter, explained!

I'm writing the introduction for my thesis and reading the Book, 'Galaxy Formation and Evolution' by Mo et al. There is a clear and accessible explanation of what the σ_8 parameter really means:
In the linear regime the density field ρ is Gaussian, characterised by the scale-invariant Harrison-Zel'dovich spectrum. It means that the power of a mode P(k) ∝ k^(n - 1), and n = 1. This ensures that the gravitational potential does not diverge neither on small nor on large scales.
In order to fully specify the density field in the early Universe we have to observationally constrain the amplitude of the H-Z spectrum. This amplitude sets the amount of clustering of structure, frequently estimated from the two-point correlation function.
When someone measures σ_8 from galaxy clustering now it means that he or she has calculated the variance (difference from the background density) of galaxy number counts within randomly placed spheres with radius R = 8h^-1 Mpc. For galaxies of Milky Way luminosity the variance is ~= 1, however, such variance decreases sharply if the radii of such spheres approach 30h^-1 Mpc. This means that the Universe is non-homogeneous on small scales, but approaches homogeneity on larger ones.
Note that the cosmological parameter σ_8 and the observed galaxy number variance in spheres of radius 8h^-1 Mpc are not equivalent. The structures we observe today are very far in the non-linear regime.

Daily Paper #10: Reconstructed density and velocity fields from the 2MASS Redshift Survey

Today's article was referenced to in the WISE TF paper I summarised yesterday. I wanted to find out how the peculiar velocities and density fields were reconstructed.
Title: Reconstructed density and velocity fields from the 2MASS Redshift Survey
Authors: Erdoğdu, Lahav et al.
Year: 2006, http://mnras.oxfordjournals.org/content/373/1/45.full
I have to admit I did not understand the mathematics of this article, and will read Peebles 1973 and Fisher 1995 to understand what are the spherical harmonics and Fourier-Bessel functions in detail. What they do in order to transform the the redshift space to the real space is decompose the redshift space distribution into radial and angular components. Peculiar velocities affect only the radial component, so it is easier to deconvolve them.
The relationship between mass and light distribution is usually assumed to be linear with some proportionality constant (there is an article by Vivienne arguing that this is not the case).
They provide density and velocity maps up to cz = 16 0000 km/s, which covers the CALIFA redshift range. I could ask them for the velocity data and obtain the peculiar velocities/infall corrected distances for the sample. I think it would be useful for me later, when working with the density fields and spin alignments. We would also have these distances and their errors for all the galaxies, not only the ones identified as belonging to structures.
Previously I used the Virgo-GA-Shapley infall corrected redshifts from NED (obtained using this model: http://iopscience.iop.org/0004-637X/529/2/786/fulltext/). It's a simpler model, taking only these three attractors into account.

Daily Paper #8: Constraints on the relationship between stellar mass and halo mass at low and high redshift

Title: Constraints on the relationship between stellar mass and halo mass at low and high redshift
Authors: Moster, Somerville et al.
Year: 2009, http://arxiv.org/abs/0903.4682
They give a nice breakdown of the methods used to link the halo properties with those of the galaxy. It is possible to obtain these relations from observations (kinematics, lensing, X-rays), from bottom-up modelling (N-body or SAMs), or by using a statistical approach: obtaining the probability that a halo with a certain mass hosts a certain number of galaxies with some certain properties (luminosity, type, etc.). This way, we don't have to make assumptions about feedback and other poorly-understood processes that plague the SAMs. I'll review the lecture recordings from Jerusalem School, I think the formalism used was explained in detail there.
The goal of this paper is to construct the conditional stellar mass function (as opposed to the conditional luminosity function). Such a function provides the average number of galaxies in a certain stellar mass range that reside in a halo with a mass M -- it can also be viewed as the stellar mass function for the haloes of mass M.
They use a N-body simulation to obtain a population of DM haloes and their merger tree information. The ratio of the halo mass M and the stellar mass M is not constant (due to different feedback processes), so they use a parameterisation of it to fill the haloes with galaxies, and obtain the stellar mass-Mhalo relation.
In order to obtain the conditional mass function, they divide the galaxies into centrals and satellites, parameterising their distribution in two different ways. The total CMF is the combination of the two.
They also obtain the M* -- M_halo relationship for higher redshifts, claiming that 'large halos accrete dark matter faster than large galaxies grow in stellar mass, while the growth of low mass halos is slower than that of the central galaxies they harbor', (see the attached picture).

This paper does not mention the TF relation, however, I wanted to find out more about the M*-Mhalo relation, the ways to determine it and its evolution. It's interesting that the high-mass end of this relation does not evolve much since z=4.

Daily Paper #4: Dark halo response and the stellar initial mass function in early-type and late-type galaxies

Our group meeting ate most of my day, so here's a delayed review. Title: Dark halo response and the stellar initial mass function in early-type and late-type galaxies
Authors: Dutton, Conroy, van den Bosch et al., http://arxiv.org/abs/1012.5859
Year: 2011
The authors try to find the origins of the TF and Faber-Jackson relations, using a big sample of observed galaxies from SDSS, a set of observational scaling relations showing the distribution of baryons in galaxies, with constrains on the DM halo structure from simulations.
They claim in the introduction that the origin of TFR and FJR is the relation between the halo virial velocity and its virial mass, which scales as v_vir \propto M^(1/3). The relation between v_opt (*) and v_vir depends on 3 factors:
-- the contribution of baryons to v_opt
-- the structure of pristine (DM-only) haloes. The halo profiles are well-enough defined by the NFW profile.
-- and the halo response to the disk formation (contraction/expansion)
The biggest source of uncertainty for the first factor is the IMF, as most of the baryonic mass in galaxies (except the low-mass star-forming ones) is in stars.
The third factor, the halo response, is quite uncertain. It can be adiabatic or non-adiabatic contraction, or expansion due to a number of different processes.
They use a large number of observed relations (TF and FJ relations too) to constrain or predict unknown quantities in their analytic model, modelling the DM halo, bulges, disks, gas disks, constructing 3D models of their SDSS sample galaxies (~100 000 LTGs, ~160 000 ETGs).
They construct mass models for all those galaxies using various IMF and assumptions about the halo response. Then they compare them with the observed circular velocity -- stellar mass relations (I do not understand it at this point -- they already used the TFR as a constraint while solving for the halo contraction at a given IMF, so it is inbuilt in their model somehow?).
Nevertheless, they do not reproduce the zero-point of the TFR with the standard Chabrier IMF and standard adiabatic halo contraction model, as the velocity is overpredicted. They claim that it is possible to fix that by either assuming a different IMF, or changing the halo response, or having different halo concentrations (set by formation time or \sigma_8, they claim that both ways to do it do not solve the zero-point problem).
However, they find that early-type and late-type galaxies cannot have the same IMF and halo response. For any given halo response model, ETGs and LTGs must have different IMF normalisations to reproduce the TFR. If we assume a universal IMF, early-type galaxies require stronger halo contraction.
They look into the model circular velocity profiles (see attached) for models that reproduce the TF and FJRs, with Chabrier IMF. The velocity profiles look rather constant at higher radii, reaching the maximum at ~0.3 R_vir. (For the LTGs, they convert the velocity dispersion to v_circ picking a rather simple conversion factor between sqrt(2) and sqrt(3).) They claim that the flatness of the rotation curves does not depend strongly on the IMF and the halo response model, and 'is a natural consequence for galaxies embedded in LCDM haloes'.
Then they discuss possible mechanisms that would account for differences in IMF or halo response for ETGs and LTGs. The halo contraction/expansion may depend on galaxy morphology via a number of processes:
-- adiabatic contraction due to smooth accretion -- results in disk growth and SF, important for LTGs
-- wet major mergers -- result in halo contraction because gas settles in the center of a galaxy, transforms LTGs to ellipticals
-- dry major mergers ( for ETGs) -- halo contraction due to violent relaxation which mixes stars and DM
-- clumpy accretion/minor mergers: halo expansion due to dynamical friction. Clumps must be baryonic, so that's likely to occur at high redshifts (A. Dekel was arguing in Jerusalem that it must be the case).
-- feedback causes halo expansion, more important to LTGs and for higher redshifts.
-- bars -- halo expansion or contraction, not clear.

They sum it all up by saying that the key formation event that distinguishes ETGs from LTGs is a major merger (dry or wet), which causes halo contraction. For LTGs, haloes could expand due to a combination of clumpy cold accretion and intensive feedback.
The IMF may plausibly vary with redshift due to its alleged dependence on ISM temperature via the Jeans mass. Since ETGs form their stars earlier than LTGs, their IMF might be different. They discuss the van Dokkum & Conroy 2008 article on the different IMF at the cores of massive ellipticals, and conclude that this IMF would not fit for the other ETGs well.
All in all, they show that there is a degeneracy between IMF and the halo response to disk formation, and we cannot match the two for ETGs and LTGs if we want to reproduce the TFR. However, I'm puzzled here -- like in the previous Mo, Mao, White article, they do not model galaxy evolution in a self-contained way, and a model cannot show things that are not included in it. Mo, Mao & White include one set of parameters in their article, and get a set dependences on their parameters (like the disk formation time). Here Dutton et al. model rotation curves as functions of other parameters, and get dependence on another set of parameters. I think it's tricky to understand which parameters are really important, because in astrophysics we often have many coupled parameters, and it's not difficult to find correlations between them. It's more difficult to find out which ones are the fundamental ones, which really affect the TFR.
-- a question: what does it mean "TFR is an edge-on projection of the fundamental plane" (p. 323)?
(*) v2.2 for late-type galaxies and some measure of velocity proportional to dispersion at the effective radius for early types

Daily Paper #3: Rotation rates, sizes and star formation efficiencies of a representative population of simulated disc galaxies

I was a bit late today, because I went to see a couple of talks at the HETDEX meeting. A couple of interesting points from there:
-- The LAE people are worried about selection bias arising due to galaxy spins' alignment with the large scale structure (http://arxiv.org/abs/1004.3611)
-- Cluster growth depends not only on the proto-cluster environment (i.e. the immediate neighbourhood), but on super-halo scales as well (it's probably better defined here: http://arxiv.org/abs/1109.6328)

...On to the paper:
Title: Rotation rates, sizes and star formation efficiencies of a representative population of simulated disc galaxies
Authors: McCarthy, Schaye et al.
Year: 2012, http://arxiv.org/abs/1204.5195 They use resimulated (SPH) Millenium sub-regions with selected representative mean densities, including baryonic physics. They include background UV/Xray radiation field that 'reionises' the simulations at z = 9 and the CMB. They model star formation using an effective prescription reproducing the Kennicut's relation and assuming Chabrier IMF, as well as yields and timing of nucleosynthesis and SN feedback.
Then they fit the surface brightness profiles of galaxies in 9 - 11.5 log M* range with a Sersic function and classify their galaxies into disc and spheroid-dominated usin n = 2.5 as the cut.
-- The stellar mass - rotation velocity relation:
They examine this relation for their disk galaxy population (see the attached picture) and compare it with Reyes 2011 observations, claiming that this is the first cosmological hydrodynamical simulation that produces a population of galaxies consistent with the observed TFR. The slope is slightly higher, but in general, the agreement is really good. They use v80 (velocity at 80% light radius) and Vmax as the velocity measures. The velocities at their high-mass range are too big, and they claim that lack of prescription for AGN feedback may explain that.
The authors also discuss the scatter in TF relation, claiming that it is not possible to directly compare observed and simulated TF scatter without careful analysis of selection criteria and observational uncertainties.
Simulated spheroid galaxies follow the TFR well at this mass range, except for the most massive galaxies. The rotation curves of the galaxies with M* > 10.6 are not realistic (due to overcooling, too efficient SF of the highest mass haloes). Their simulated galaxies are also compatible with observed M* - size and star formation efficiency -- M* relations, up to the higher mass range.
One more quantity that simulations are compared with is the ratio of v_circ to v_200. If there is no significant halo expansion/contraction, this ratio should be roughly equal to 1.2 (Duffy 2010 writes more on halo expansion/contraction issue and impact on this ratio). Again, their results agree with this quite well up to log(M*) > 10.5.
They try to reproduce the main galaxy sequence at z = 0, comparing their results with SFR from Galex. Except for the lowest mass galaxies where their resolution is too small, it works well.
The section 4 is an interesting discussion of connection between SF efficiency, stellar mass function and the TF relation. They show that by assuming power-law shapes for halo mass function and stellar mass function in certain stellar mass range where this is valid, it is possible to match haloes (=velocities) and stellar masses using the abundance matching method, and reproduce TFR and SFR efficiency-M200 relations well (and maybe even constrain the faint end of the IMF). The way I understand it, the TFR arises due to the linear (in log-space) match between the halo mass function (set by cosmology) and the stellar mass function (set by IMF, SFR efficiency, thus feedback, etc.). I'll read Mo, van den Bosch and White 2010 for more discussion on this matter.

Daily Paper #2: The Tully-Fisher Zero Point Problem

Today's is a short paper (conference proceedings, just 4 or so pages), dealing with the halo contraction/expansion issue.

Title: The Tully-Fisher Zero Point Problem
Authors: Dutton, van den Bosch & Courteau
Year: 2008, http://arxiv.org/abs/0801.1505

The authors claim that CDM-based disk formation models can reproduce the slope/scatter of the TFR, however, its zeropoint has not been matched. This problem gets even worse if additional constraints (disk sizes, number densities) are imposed.
The TFR zeropoint can be matched in models if the halo contraction or disk self-gravity are not taken into account, or, as is shown in the article, halo contraction is counteracted by baryon feedback. They model an exponential disk in a NFW halo, obtain its luminosity from observed TFR and its scale-length from the size-luminosity relation. Assuming WMAP3 cosmology and a concentration parameter value from simulations, they solve for the virial mass and obtain rotation curves with and without the halo contraction (see the attached plot). The halo-contraction case is in conflict with both theory and observations, meaning that the halo is too small and has too high spin parameter.
They suggest 3 ways to solve this problem:

• -- lower the stellar mass-to-light ratio (but there is no known IMF that could provide that). Also, they claim that baryons at the disk and bulge account for at least half of the v2.2 -- I didn't know that (Courteau 1999, Weiner 2001)!
• -- lower the initial concentration (then the virial radius of a halo is increased) -- but that's incompatible with WMAP3 cosmology.
• -- turn off or reverse halo contraction: disk galaxies do not form in isolated haloes by smooth cooling. Halo contraction can be reversed by:
  • a) Feedback during adiabatic disk formation, if a large fraction of its mass is removed. It would also explain why galaxy formation is so inefficient (I think they mean that the gas is not converted into stars rapidly).
  • b) Dynamic friction between baryons and DM due to bars or large baryonic clumps (do they mean violent disk instabilities here?). They do not explain the details of such a process here, but I think what happens is that baryons transfer some of their angular momentum to the halo due to formation of massive, concentrated, rapidly moving structures.

The interesting message of the article is that the TFR zeropoint can provide clues into baryon feedback (which should also explain the core-cusp problem of DM haloes, at least that was what A. Dekel and J. Primack maintained at the Jerusalem Winter School). That's important.

Daily Paper: The formation of galactic discs

Me and my supervisor agreed that I would read a paper a day and write it up, so I'll be copying the summaries here.

Title: The formation of galactic discs (http://adsabs.harvard.edu/abs/1998MNRAS.295..319M)
Authors: Mo, Mao, White
Year: 1998
It's actually a really important paper -- I'm glad not to have missed it. They model galactic disk formation (of pure exponential ones, though they address influence of a simple bulge model later) in 3 CDM cosmologies. The authors make 4 important assumptions:
1) The mass of a disk is a fixed fraction of its halo
2) The angular momentum of the disk is also a fixed fraction of that of the DM halo (later they find that the specific angular momenta of the disk and halo are similar, so these two ratios should be equal).
3) The disk is thin, has an exponential density profile and is centrifugally supported
4) Real galaxies are dynamically stable disks, i.e. they reject unstable models.

They calculate the halo mass function using Press-Schechter formalism (see Appendix), assume halo angular momentum distribution determined by N-body simulations and a constant mass-to light ratio, and NFW profile. They calculate the total energy of a truncated (to r_200) NFW halo using the virial theorem, the rotation curve corresponding to it (after accounting for adiabatic halo contraction and gravitational disk influence).
See the attached picture (Mo1998_rotcurves.png) for their results. They claim that the shape of a rotation curve depends on 3 parameters only: the halo concentration parameter c(see *), fraction of mass in the disk m_d, and the spin parameter.

There is a lot more in this paper, but they devote a significant section of it to Tully-Fisher relation, explaining the origins of its slope, zeropoint and intrinsic scatter.

• -- slope: They claim that it is a generic prediction of hierarchical structure formation models with CDM-like fluctuation spectra (which set the halo formation times and thus their concentration c distribution).
• -- zeropoint: mostly set on disk mass fraction, mass-to-light radio and the redshift at which a given disk was assembled. They claim that disks must have effectively formed at redshifts close to zero (?), unless we assume an unphysical mass-to-light ratio.
• -- scatter: they analyse possible sources of intrinsic scatter of the disks, and find that:
  • --- a small amount of scatter comes from the spin parameter distribution
  • --- scatter in concentration c also adds scatter to the TF relation (disks at more concentrated haloes spin faster).
  • --- bulge is not included in their model, so bulge luminosity contribution is not accounted for -- that's a source of scatter as well
  • --- mass-to-light ratio may vary, adding some more scatter
  • --- formation times may vary as well, adding even more scatter.

The intrinsic scatter because of the first two factors cannot be smaller than 0.15 mag.
In conclusion, they show that it is possible to derive a realistic TF relation theoretically, however, I'm not sure if that is the only way it could arise? They do not include bulges, which are important for our sample, too. I am also unsure what do they mean with 'effective disk assembly redshift' at z <= 1.

* c == r_200/r_s, here r_200 -- the limiting radius of a halo, defined so that the mean density inside this radius is 200 times larger than the background density, r_s -- the disk scale length.
There is also a brief explanation of the \sigma_8 parameter -- see attached.

lit: Spins and orientations of haloes in cosmic filaments

Zhang et al., many useful references on methods therein.

Jerusalem WS lecture notes: 10. Formation and Mergers of Massive black Holes

By Avi Loeb, slides here.

• why most of the matter is not BHs? Due to angular momentum of collapsing matter <- tidal torques from neighbours near turnaround <- non-spherical collapse
• you can check in, you can't check out
• fill the orbit of Earth w/ water -> black hole from a huge swimming pool in space
• pathological point in space-time
• 'string theorists still get paid, get prizes, they give prizes to each other'
• no hair theorem: charge is not important in astrophysics, only mass and spin
• cosmic censorship conjecture (no naked singularities)
• Beckenstein-Hawking radiation: negligible in astrophysics
• whenever there is a horizon, there are quantum fluctuations
• SgrA* 3D star orbits
• horizon commercial
• Broderick & Loeb 2006 - imaging SgrA*, cosmological beaming due to lensing
• BH spin parameter - max value is c, a = 1, normalisation (spin matters!)
• shadow of the BH: the region behind it has its light obscured
• gas is optically thin for wavelengths < 1mm
• ISM does not blur the image due to free e- scattering (turbulence), blurring is smaller than horizon scale
• VLBA can resolve SgrA* and M87 (~10 u-arcsecs)
• the Event-Horizon Telescope
• radio: Fourier space imaging, Broderick, Loeb 2010
• M87: huge BH, jet base images, Doeleman 2012
• feeding BH: MR instabilities, funnel (empty region for outflow, collimated by outflowing jet)
• Eddington limit: Thompson scattering due to luminosity of BH accretion -> outward force, momentum flux, Thompson cross-section. Protons are pulled by gravity create inward force, they are balanced at Eddington luminosity L_E = 1.3x 10^{38} erg/s (M/M_{\odot})
• BH luminosity: L_E x \eta: mass of BH grows exponentially
• Eddington timescale: short, we can grow a small seed to large value quickly. By trapping radiation, timescales shorten
• hot haloes collapse to supermassive stars -> BHs
• 1% of galaxies are quasars, BH mass is way lower than the total mass of the host: why are quasars short-lived? Because they are suicidal, self-regulating their growth, unbinding the gas that is feeding them.
• 10% quasars have jets (are radio loud)
• Binary AGN (Shen 2011)
• BL regions: characteristic speeds ~0.01c, UV radiation is converted into broad line emission
• NL regions: ~1kpc distance, gass is illuminated by quasar
• merger: at some stage, it can have 1 NL region and 2 BL region. Blech, Loeb 2012
• reverberation mapping, Koessis, Heiman, Loeb
• residence time of BHB - types of migration, shrinks the orbit differently from GWs
• Kulkarni & Loeb: excursion set formalism, multiple BHs: 3 body system is unstable (like human beings)
• SF in outer regions of accretion disk - you're likely to make stars - it may explain why quasar spectra have metal lines!
• extreme mass ratio inspiral stellar mass BH or NS [LISA]
• gravitational waves - time-dependent quadrupoles, BH/NS binaries, LIGO, eLISA (detects virtual GWs, generated by people playing WoW) -> precision: 1/1000th diameter of proton
• BH recoils: if the BHs have different masses, they recoil at hundreds km/s - they get out of the galaxy or move away from the center. GW emission is beamed at one direction, momentum is conserved
• > kick, candidate CID-42
• Star clusters around recoiled BHs in the MW halo: ~100 BHs ejected during assembly of MW halo, carrying SCs from cusp of host dwarf galaxy - there should be some unusual clusters in halo clusters, O'Leary & Loeb 2008. Stars are moving around BH Keplerian potential, BH gets a kick, stars may remain bound by E = -1/2 v^2 - GM/r^2 = 0.5(v - v_{kick} - GM/r^2) (vector addition), if E remains negative
• tidal disruption of stars by BHs ('this is an illustration from NASA, so it has no scientific value')
• loss cone: tidal disruption 1/10^{-5}
• BHs larger than 10^8 M_{\odot} swallow the whole stars - Hayasaki, Stone, Loeb 2012
• for binaries: loss cone filled by GW recoil, star disruption once every 10-100 years
• miniquasar 2013 - cloud falling into SgrA*, pericenter of highly elliptical, almost radial orbit with T == 200 yr, imsged in Br\gamma -- Burkert 2012 simulation
• is the cloud pressure-confined? There seems to be no evidence of ambient ram pressure? Maybe this cloud is produced by low mass star with protoplanetary disk - Murray-Clay & Loeb 2012
• hypervelocity planets from tidal disruption of stellar binaries

lit: a few articles by FvdB

One of our lecturers, Frank van den Bosch, pointed me to a few articles that might be useful for the topics I'm currently studying:
Spatial and kinematic alignments between central and satellite halos
Probing the Intrinsic Shape and Alignment of Dark Matter Haloes using SDSS Galaxy Groups
The Tully-Fisher Zero Point Problem